{"revision":"c10276e953456835cdbb1f3a60d58ae1980be353","document":{"id":30283,"path":"it-operations-management/event-management/c_EMEventIdentifier.md","title":"Event identifiers","bundle":null,"doc_type":null,"release":"australia","body":"\n# Event identifiers\n\nEvent identifiers uniquely distinguish one event from another. Event Management uses these identifiers to determine whether to create a new alert or update an existing one.\n\nBy default, an event is uniquely identified by the following fields:\n\n-   **Message Key**\n-   **Domain**\n-   **Category**\n\nChanging the **Category** field \\(for example, through a Background Script or Business Rule\\) may lead to unexpected system behavior.\n\nIf the **Message Key** is not provided, the system automatically generates one by concatenating the following fields:\n\n-   **Source**\n-   **Type**\n-   **Node**\n-   **Resource**\n-   **Metric Name**\n\nIf the above fields are not defined in the incoming event, you can define them using event rules.\n\n"}}